Denitrification treatment agent, denitrification treatment method, and denitrification treatment apparatus

Abstract

To provide a denitrification treatment agent, a denitrification treatment method, and a denitrification treatment apparatus capable of efficiently denitrifying nitrogen-containing wastewater with a simple configuration without the need for hydrogen donor injection control.SOLUTION: The denitrification treatment agent is composed of fiber moldings formed into a specific shape containing rayon fibers with a fiber diameter of 100 μm or less, which is used for denitrification treatment of nitrogen-containing wastewater.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a denitrification treatment agent, a denitrification treatment method, and a denitrification treatment device, and in particular to a denitrification treatment agent supplied as a hydrogen donor in a biological treatment method for nitrogen-containing wastewater, and a denitrification treatment method and a denitrification treatment device using the same. [Background technology]

[0002] Organic wastewater containing nitrogen such as nitrogen compounds (hereinafter referred to as "nitrogen-containing wastewater") is generally treated using biological treatment. A typical denitrification treatment flow is shown in Figures 10 and 11.

[0003] 10 shows an example of a treatment flow for removing nitrogen from nitrogen-containing wastewater containing nitrate nitrogen or nitrite nitrogen. The denitrification treatment device comprises a denitrification treatment tank 1100, an aeration tank 1300, and a solid-liquid separation tank 2000 such as a settling tank. Nitrogen-containing wastewater containing nitrate nitrogen or nitrite nitrogen is flowed into the denitrification treatment tank 1100. In the denitrification treatment tank 1100, returned sludge from the solid-liquid separation tank 2000 and a hydrogen donor such as methanol are added, and the nitrate nitrogen in the nitrogen-containing wastewater is converted into nitrogen gas, thereby removing nitrogen from the nitrogen-containing wastewater.

[0004] The denitrification treatment liquid obtained in the denitrification treatment tank 1100 is introduced into the aeration tank 1300. In the aeration tank 1300, air is introduced into the bottom of the aeration tank 1300 to remove BOD resulting from hydrogen donors remaining in the denitrification treatment liquid. In the solid-liquid separation tank 2000, the aeration treatment liquid flowing out from the aeration tank 1300 is separated into separated sludge and treated water. A portion of the separated sludge obtained by solid-liquid separation is returned to the denitrification treatment tank as returned sludge, and the remaining sludge is treated as excess sludge and undergoes predetermined treatment such as dehydration. The treated water is either discharged into a sewerage system or subjected to advanced treatment again for reuse.

[0005] 11 shows a treatment flow for removing nitrogen from nitrogen-containing wastewater containing organic nitrogen such as ammonia nitrogen, nitrate nitrogen, or nitrite nitrogen. This denitrification treatment apparatus comprises a nitrification treatment tank 500, a denitrification treatment tank 1100, an aeration tank 1300, and a solid-liquid separation tank 2000 such as a settling tank. In the nitrification treatment tank 500, in the presence of dissolved oxygen (hereinafter referred to as DO), ammonia nitrogen and organic nitrogen from the nitrogen-containing wastewater are oxidized to nitrate nitrogen and nitrite nitrogen by nitrifying bacteria in the activated sludge of the return sludge. As nitrification progresses, the pH decreases, and a decrease in pH reduces the activity of nitrifying bacteria, so an alkaline agent such as caustic soda is added to the nitrification treatment tank 500.

[0006] In the denitrification tank 1100, the nitrate nitrogen and nitrite nitrogen in the nitrified liquor flowing out from the nitrification tank 500 are treated with denitrifying bacteria and a hydrogen donor such as methanol, generating and removing the nitrate nitrogen and nitrite nitrogen as nitrogen gas. In the aeration tank 1300, the BOD derived from the residual methanol contained in the denitrification treated liquor flowing out from the denitrification tank 1100 is removed by oxidation. In the solid-liquid separation tank 2000, the aeration treated liquor flowing out from the aeration tank 1300 is separated into separated sludge and treated water.

[0007] In a denitrification treatment apparatus such as that shown in Figure 10 or 11, it is essential to add an organic carbon source as a hydrogen donor so that denitrifying bacteria in the denitrification treatment tank 1100 can reduce nitrate nitrogen and nitrite nitrogen (NOx-N) to nitrogen gas (N2). Known hydrogen donors include those that use carboxylic acids with three or fewer carbon atoms, as described in Japanese Patent Laid-Open No. 6-126298 (Patent Document 1). Also known is a hydrogen donor in which a linear saturated monocarboxylic acid with six or more carbon atoms is supported on a support, as described in Japanese Patent Laid-Open No. 2000-334492 (Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-126298 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-334492 Summary of the Invention [Problem to be solved by the invention]

[0009] However, when using methanol or the like as a hydrogen donor as described in Patent Document 1, the hydrogen donor has a high solubility in nitrogen-containing wastewater, and there is a problem of difficulty in controlling injection because there is no commercially available monitoring device that can accurately measure the nitrate nitrogen concentration or nitrite nitrogen concentration in nitrogen-containing wastewater. On the other hand, higher fatty acids and higher alcohols as described in Patent Document 2 are solid and therefore less soluble in water. Furthermore, hydrogen donors such as higher fatty acids dissolve depending on the nitrate nitrogen concentration or nitrite nitrogen concentration in the nitrogen-containing wastewater to be denitrified, making injection control less difficult compared to when using methanol or the like. Therefore, they have the advantage of being easily usable as hydrogen donors. However, if solid granular or flaky hydrogen donors are used as they are, they may flow out with the treated water. In some cases, solid granular or flaky hydrogen donors may be discharged out of the system with sludge during the solid-liquid separation process, resulting in significant waste of the hydrogen donor.

[0010] In view of the above problems, the present invention provides a denitrification treatment agent, a denitrification treatment method, and a denitrification treatment device that do not require control of injection of a hydrogen donor and that can efficiently denitrify nitrogen-containing wastewater with a simple configuration. [Means for solving the problem]

[0011] As a result of intensive research to solve the above problems, the present inventors have found that it is effective to use a denitrification treatment agent composed of a fibrous molded product containing rayon fibers molded into a specific shape, instead of methanol, which has conventionally been added as a hydrogen donor.

[0012] In order to solve the above problems, in one aspect, the present invention provides a denitrification treatment agent used for denitrification treatment of nitrogen-containing wastewater, which is composed of a fibrous molded body molded into a certain shape and containing rayon fibers having a fiber diameter of 100 μm or less.

[0013] In one embodiment of the denitrification treatment agent according to the present invention, the fiber molding comprises a support for supporting rayon fibers, and the fiber molding has any one of the following shapes: rectangular parallelepiped, cubic, cylindrical, columnar, block, plate, membrane, lattice, or string-like with both ends of rayon fibers bundled together.

[0014] In another aspect, the present invention provides a denitrification method in which nitrogen-containing wastewater is introduced into a denitrification tank containing a denitrification agent composed of a fibrous molding formed into a fixed shape and containing rayon fibers with a fiber diameter of 100 μm or less, the tank is stirred, and the nitrogen-containing wastewater is denitrified while being brought into contact with the denitrification agent, and the denitrification liquid obtained by the denitrification treatment is subjected to solid-liquid separation.

[0015] In yet another aspect, the present invention provides a denitrification method comprising: nitrifying nitrogen-containing wastewater in the presence of nitrifying bacteria; introducing a nitrified liquid obtained by the nitrification treatment into a denitrification treatment tank containing a denitrification treatment agent composed of a fibrous molded body formed into a fixed shape and containing rayon fibers with a fiber diameter of 100 μm or less; denitrifying the nitrified liquid in the presence of denitrifying bacteria while stirring the denitrification treatment tank to bring the nitrified liquid into contact with the denitrification treatment agent; and performing solid-liquid separation of the denitrified liquid obtained by the denitrification treatment.

[0016] In one embodiment of the denitrification method according to the present invention, nitrogen-containing wastewater is subjected to denitrification treatment before nitrification treatment.

[0017] In yet another aspect, the present invention provides a first denitrification treatment method, which comprises: a first solid-liquid separation treatment for separating nitrogen-containing sludge into solid and liquid; a first denitrification treatment method in which the separated liquid obtained in the first solid-liquid separation treatment is introduced into a first denitrification treatment tank containing a denitrification treatment agent composed of a fibrous molded body formed into a specific shape containing rayon fibers having a fiber diameter of 100 μm or less, and the first denitrification treatment tank is stirred to denitrify the separated liquid while bringing the separated liquid into contact with the denitrification treatment agent; and a first denitrification treatment method in which the first denitrification treatment treatment liquid obtained in the first denitrification treatment is introduced into a first denitrification treatment tank containing a denitrification treatment agent composed of a fibrous molded body formed into a specific shape containing rayon fibers having a fiber diameter of 100 μm or less, and the first denitrification treatment tank is stirred to denitrify the separated liquid while bringing the separated liquid into contact with the denitrification treatment agent. The denitrification method includes a nitrification treatment in which nitrification treatment is performed in the presence of nitrifying bacteria, a second denitrification treatment in which the nitrified liquid obtained in the nitrification treatment is introduced into a second denitrification treatment tank and the nitrified liquid is denitrified in the second denitrification treatment tank in the presence of denitrifying bacteria, a second solid-liquid separation treatment in which the second denitrification treatment liquid obtained in the second denitrification treatment is separated into solid and liquid, and a return treatment in which the separated sludge separated in the second solid-liquid separation treatment is returned to at least one of the first denitrification treatment and the first solid-liquid separation treatment.

[0018] In yet another aspect, the present invention provides a denitrification method in which nitrogen-containing wastewater is introduced into an aerobic denitrification treatment, a denitrification treatment agent is introduced into the aerobic denitrification treatment, the denitrification treatment agent is a fibrous molded body formed into a specific shape and containing rayon fibers with a fiber diameter of 100 μm or less, air is supplied to bring the nitrogen-containing wastewater into contact with the denitrification treatment agent, and the aerobic denitrification treatment liquid is subjected to solid-liquid separation.

[0019] In yet another aspect, the present invention provides a denitrification treatment device comprising: a denitrification treatment means for denitrifying nitrogen-containing wastewater in the presence of denitrifying bacteria, the denitrification treatment agent being made of a fibrous molded body formed into a fixed shape and containing rayon fibers with a fiber diameter of 100 μm or less; a stirring means for agitating the nitrogen-containing wastewater supplied to the denitrification treatment means and bringing the nitrogen-containing wastewater into contact with the denitrification treatment agent; and a solid-liquid separation means for performing solid-liquid separation of the denitrification treatment liquid treated in the denitrification treatment means.

[0020] In yet another aspect, the present invention provides a denitrification treatment apparatus comprising: nitrification treatment means for introducing nitrogen-containing wastewater and nitrifying it; denitrification treatment means for denitrifying the nitrified liquid obtained by the nitrification treatment means in the presence of denitrifying bacteria, the denitrification treatment agent being made of a fibrous molded body formed into a fixed shape and containing rayon fibers having a fiber diameter of 100 μm or less; stirring means for stirring the nitrified liquid and bringing the nitrified liquid into contact with the denitrification treatment agent to obtain a denitrified liquid; and solid-liquid separation means for separating the denitrified liquid into solid and liquid.

[0021] In yet another aspect, the present invention provides a denitrification treatment apparatus comprising: a first denitrification treatment means for denitrifying nitrogen-containing wastewater or nitrogen-containing sludge in the presence of denitrifying bacteria, the first denitrification treatment means comprising a denitrification treatment agent made of a fibrous molded body formed into a fixed shape and containing rayon fibers with a fiber diameter of 100 μm or less, to obtain a first denitrification treatment liquid; a nitrification treatment means for nitrifying the first denitrification treatment liquid; a nitrification liquid return means for returning the nitrification liquid obtained by the first denitrification treatment means; a second denitrification treatment means for contacting the nitrification liquid obtained by the nitrification treatment means with a denitrification treatment agent made of a fibrous molded body formed into a fixed shape and containing rayon fibers with a fiber diameter of 100 μm or less, to obtain a second denitrification treatment liquid; and a solid-liquid separation means for performing solid-liquid separation of the second denitrification treatment liquid and obtaining returned sludge to be returned to the first denitrification treatment means.

[0022] In one embodiment, the denitrification treatment apparatus according to the present invention further comprises, upstream of the first denitrification treatment means, a concentration / dehydration treatment means for dehydrating and concentrating nitrogen-containing wastewater or nitrogen-containing sludge, and an excess sludge return means for returning excess sludge obtained in the solid-liquid separation means to a coagulation tank or concentration / dehydration treatment means provided upstream of the concentration / dehydration treatment means. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a denitrification treatment agent, a denitrification treatment method, and a denitrification treatment apparatus that can efficiently denitrify nitrogen-containing wastewater with a simple configuration without requiring control of injection of a hydrogen donor. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is an explanatory diagram showing one embodiment of a denitrification treatment agent according to an embodiment of the present invention. [Figure 2] 1 is a photograph showing an example of rayon fiber that can be used in a denitrification treatment agent. [Figure 3] 1 is an explanatory diagram showing an example of the configuration of a denitrification treatment agent suitable for storing the denitrification treatment agent in a denitrification treatment tank according to an embodiment of the present invention. FIG. [Figure 4] 1 is a schematic diagram showing an example of a denitrification treatment method and a denitrification treatment device for nitrogen-containing wastewater according to an embodiment of the present invention. [Figure 5] 1 is a schematic diagram showing an example of the configuration of a denitrification treatment tank according to an embodiment of the present invention. [Figure 6] FIG. 1 is a schematic diagram showing an example of a denitrification treatment method and denitrification treatment apparatus for nitrogen-containing wastewater according to a first modified example of an embodiment of the present invention. [Figure 7] FIG. 10 is a schematic diagram showing an example of a method and apparatus for denitrifying nitrogen-containing wastewater according to a second modified example of an embodiment of the present invention. [Figure 8] FIG. 10 is a schematic diagram showing an example of a denitrification treatment method and denitrification treatment apparatus for nitrogen-containing wastewater according to a third modified example of an embodiment of the present invention. [Figure 9] FIG. 10 is a schematic diagram showing an example of a denitrification treatment method and denitrification treatment apparatus for nitrogen-containing wastewater according to a fourth modified example of the embodiment of the present invention. [Figure 10] 1 is a schematic diagram showing an example of a conventional denitrification treatment method and denitrification treatment apparatus for nitrogen-containing wastewater. [Figure 11] 1 is a schematic diagram showing an example of a conventional denitrification treatment method and denitrification treatment apparatus for nitrogen-containing wastewater. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. Note that the embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of component parts to those described below.

[0026] (Denitrification treatment agent) 1(a) to 1(d) are explanatory diagrams showing an example of the configuration of a denitrification treatment agent 100 according to an embodiment of the present invention. The denitrification treatment agent 100 according to the embodiment of the present invention is a denitrification treatment agent used for denitrifying nitrogen-containing wastewater, and is made up of a fibrous molded body 10 including rayon fibers 11a, 11b, 11c, and 11d having a fiber diameter of 100 μm or less and molded into a specific shape.

[0027] By using fine fibers with a fiber diameter of 100 μm or less as the rayon fibers 11a, 11b, 11c, and 11d, the fibers flow more easily in the liquid than when granular fibers or the like are used, thereby improving the contact efficiency with the nitrogen-containing wastewater. The fiber diameter of the rayon fibers 11a, 11b, 11c, and 11d is more preferably 80 μm or less, and even more preferably 50 μm or less. There is no particular lower limit for the fiber diameter, but from the viewpoint of handleability, it is preferably 0.1 μm or more, and more preferably 1.0 μm or more.

[0028] Although there is no limitation on the fiber length of the rayon fibers 11a, 11b, 11c, and 11d, short rayon fibers having a fiber length of 30 mm or less, or even 10 mm or less, can be used. Alternatively, depending on the shape of the fibrous molded article 10, rayon fibers 11a, 11b, 11c, and 11d having a fiber length of more than 30 mm, or even more than 100 mm, or even more than 500 mm, typically about 10 to 500 mm, can also be used.

[0029] Rayon fibers 11a, 11b, 11c, and 11d are a type of regenerated fiber and are biodegradable, which reduces the burden on the external environment compared to using chemicals such as methanol as the hydrogen donor. Furthermore, when using chemicals such as methanol as the hydrogen donor, an aeration tank 1300 must be installed downstream of the denitrification treatment tank 1100, as shown in Figures 10 and 11. However, in this embodiment, the aeration tank 1300 is not required because methanol is not used. This allows for a simpler and more compact device configuration. Furthermore, because rayon fibers 11a, 11b, 11c, and 11d are hydrophilic, they are easily compatible with nitrogen-containing wastewater and exhibit denitrification-promoting properties for a relatively long period of time.

[0030] In addition to the rayon fibers 11a, 11b, 11c, and 11d, regenerated cellulose fibers such as polynosic, cupra, and lyocell can also be used as the denitrification treatment agent 100 according to this embodiment. Examples of regenerated cellulose fibers include regenerated artificial fibers such as viscose rayon fiber and cupra rayon fiber, which use cellulose as the base polymer, and semi-synthetic regenerated fibers such as cellulose diacetate fiber and cellulose triacetate fiber.

[0031] Among these, viscose rayon fibers are preferred because they have multiple striae in the fiber direction and an irregular petal-like cross-sectional profile, resulting in a larger surface area than fibers with a smooth surface. Viscose rayon fibers are also particularly preferred as the rayon fibers 11a, 11b, 11c, and 11d used in this embodiment because they have good drainage properties and are easy to handle.

[0032] The fiber length of the rayon fibers 11a, 11b, 11c, and 11d refers to the average value of the maximum length of five fibers extracted from any position of the fiber molding that constitutes the denitrification treatment agent 100. Similarly, the fiber diameter of the rayon fibers 11a, 11b, 11c, and 11d refers to the average value of the maximum cross-sectional diameter of five fibers extracted from any position of the fiber molding that constitutes the denitrification treatment agent 100. The fiber length and fiber diameter can be measured by observing the fibers using, for example, a tabletop scanning electron microscope (Miniscope (registered trademark) TM3000, manufactured by Hitachi High-Technologies Corporation).

[0033] Although not limited thereto, the rayon fibers 11a, 11b, 11c, and 11d preferably have a moisture content of 30 to 80% by weight, and more preferably 40 to 70% by weight. If the moisture content is 30% by weight or less or exceeds 80%, significant denitrification performance may not be obtained.

[0034] The moisture content of the rayon fibers 11a, 11b, 11c, and 11d can be adjusted by known methods. For example, the moisture content may be adjusted by spraying water onto the rayon fibers 11a, 11b, 11c, and 11d. When the rayon fibers 11a, 11b, 11c, and 11d are produced by a wet spinning method, the moisture content may be adjusted by washing with a solvent, forming the rayon fibers into a fiber molded product 10 having a predetermined shape, and then squeezing or drying the fibers.

[0035] It is possible to use the rayon fibers 11a, 11b, 11c, and 11d as they are in a denitrification tank and use them as the denitrification agent 100. However, there is a risk that the rayon fibers 11a, 11b, 11c, and 11d filled in the denitrification tank will rise to the liquid surface of the denitrification tank, flow out of the denitrification tank, and become mixed into the denitrification liquid. Furthermore, there is a risk that the rayon fibers 11a, 11b, 11c, and 11d will become entangled in various devices in the treatment tanks downstream of the denitrification tank, causing blockage of the devices.

[0036] The denitrification treatment agent 100 according to the embodiment of the present invention uses a fibrous molded article 10 in which rayon fibers 11a, 11b, 11c, and 11d are molded into a predetermined shape in advance. The denitrification effect can be achieved simply by filling the denitrification treatment agent 100 in advance as a fixed bed in a denitrification treatment tank, and therefore, compared to the case where an agent such as methanol is supplied to the denitrification treatment tank, a simpler denitrification treatment can be provided that does not require control of the injection of a hydrogen donor.

[0037] There are no particular limitations on the specific shape of the fiber molded product 10. For example, the fiber molded product 10 may have various shapes, such as a rectangular parallelepiped, cube, cylinder, column, block (meaning a block-like shape with an uneven surface), plate, film (including nonwoven fabric and felt), lattice, or string-like shape formed by bundling both ends of rayon fibers 11a, 11b, 11c, and 11d.

[0038] For example, as shown in FIGS. 1(a) to 1(d), a fiber molded product 10 includes rayon fibers 11a, 11b, 11c, and 11d, and supports 12a, 12b, 12c, 12d, 13a, and 13d that support the rayon fibers 11a, 11b, 11c, and 11d.

[0039] The example shown in Figure 1(a) shows a denitrification treatment agent 100 in which bulk rayon fibers 11a (see Figure 2) consisting of short fibers with a fiber length of 30 mm or less, more preferably 10 mm or less, are sandwiched between a first support 12a and a second support 13a facing each other to form a fiber molding 10. The first support 12a and the second support 13a can be, for example, a wire mesh made of stainless steel or a perforated plate made of synthetic resin or ceramic. The materials of the first support 12a and the second support 13a may be the same or different.

[0040] For example, in the denitrification treatment tank, the side on which the rayon fiber 11a is most likely to be loaded, for example, the side on which the first support 12a is disposed, is made of a relatively strong material, while the other side on which the second support 13a is disposed is made of an inexpensive material that is weaker in strength than the first support 12a. This makes it possible to provide a denitrification treatment agent 100 that is strong and can withstand long-term use.

[0041] To improve the contact between the fibrous molded body 10 and the nitrogen-containing wastewater, it is preferable that the top and bottom of the fibrous molded body 10 have an open structure. However, to more effectively prevent the rayon fibers 11a from flowing out of the denitrification tank, supports (not shown) may also be placed at the top and bottom of the fibrous molded body 10.

[0042] Bulk rayon fibers 11a (see FIG. 2) consisting of short fibers with a fiber length of 30 mm or less, more preferably 10 mm or less, may disperse and float within the denitrification tank when directly introduced into the denitrification tank, potentially resulting in the discharge of treated water from the tank. On the other hand, if the rayon fibers 11a are contained in a bag made of nonwoven fabric, which can easily change shape under external forces, the rayon fibers 11a may become biased or clogged within the bag. As shown in FIG. 1(a), the denitrification agent 100 is configured to maintain a constant shape within the tank by using a fibrous molded body 10 having supports 12a and 13a that support the rayon fibers 11a. This prevents the rayon fibers 11a from discharging outside the denitrification tank, increases contact between the rayon fibers 11a and the nitrogen-containing wastewater, and accelerates the denitrification process within the denitrification tank.

[0043] The example shown in Figure 1(b) shows an example of a fiber molded product 10 having a configuration in which molded bodies of rayon fibers 11b, which have been previously molded into a sheet or film (nonwoven fabric or felt), are stacked in the thickness direction, and the molded bodies of rayon fibers 11b are supported by a support 12b made of a wire mesh, a perforated plate, a support pillar, etc.

[0044] In the configuration shown in FIG. 1(b), rayon fibers 11b are formed into a sheet or film and then fixed to a support 12b. Therefore, compared to the configuration shown in FIG. 1(a), the amount of bulk rayon fibers 11a (shortened fibers) that flow out of the denitrification tank is reduced, and handling is also improved. In the configuration shown in FIG. 1(b), the cylindrical supports 12b extend parallel to the longitudinal direction of the rayon fibers 11b, forming a fence-like shape. However, this configuration is not limited to this. Furthermore, the rayon fibers 11b can be formed into any shape, such as a plate, a rectangular parallelepiped, or a columnar shape. By stacking multiple such shapes at intervals, denitrification performance can be improved. The rayon fibers 11b may be wrapped around the support 12b in the longitudinal direction to further increase contact between the rayon fibers 11b and the nitrogen-containing wastewater.

[0045] The example shown in Figure 1(c) shows a fiber molded product 10 having a structure in which a columnar support 12c is arranged and fixed as a central core on the inner surface of rayon fibers 11c obtained by forming nonwoven fabric or felt-like material into multiple layers and laminating them, and then molding the resultant material into a cylindrical shape. The radial thickness of the rayon fibers 11c is not particularly limited, but can be, for example, 1 to 50 mm, or even 10 to 50 mm. In the example of Figure 1(c), the rayon fibers 11c are wound around the outer surface of the support 12c, but the rayon fibers 11c may also be fixed on the inner surface of the support 12c.

[0046] The example shown in FIG. 1(d) is a string-like fibrous molding 10 in which both ends of rayon fibers 11d are bundled. This fibrous molding 10 is made by fixing both ends of rayon fibers 11d, each having a fiber length of more than 500 mm, with supports 12d, 13d, which are made of fixing devices such as metal plates or cable ties. The fixing devices, 12d, 13d, function to prevent the rayon fibers 11d from dispersing in the denitrification treatment tank, and the material and fixing method thereof are optional. The number of rayon fibers 11d can also be determined arbitrarily. Of course, the fiber length of the rayon fibers 11d can also be adjusted appropriately to suit the dimensions and processing capacity of the denitrification treatment tank in which they are housed.

[0047] When the fibrous molding 10 shown in FIG. 1(d) is installed in a denitrification tank containing nitrogen-containing wastewater, the ratio between the maximum length (vertical length) in the vertical direction (up and down in the plane of the drawing) and the maximum length (horizontal length) in the horizontal direction (left and right in the plane of the drawing) can be any ratio, but it is preferable that the vertical length is greater than the horizontal length and that the vertical length / horizontal length ratio is 2 to 5. If the vertical length / horizontal length ratio is less than 2, sludge may accumulate in the rayon fibers 11d with use, resulting in a decrease in treatment performance. If the vertical length / horizontal length ratio is more than 5, the contact efficiency between the rayon fibers 11d and the nitrogen-containing wastewater may decrease.

[0048] As shown in Figure 3(a), it is more preferable that the denitrification treatment agent 100 be fixed to a stand 15 for placing the fiber molding 10 at a predetermined position in the denitrification treatment tank, thereby forming a unit. After use of the denitrification treatment agent 100 has been completed, the stand 15 containing the denitrification treatment agent 100 can be lifted up to the water surface from the denitrification treatment tank, facilitating replacement. There is no limit to the number of stands 15, and two stands 15 may be used as long as replacement work is not hindered, and the stands 15 may be rod-shaped or rail-shaped.

[0049] The stand 15 allows the fiber molded body 10 to withstand water currents such as aeration in the denitrification tank and facilitates replacement work from the top of the denitrification tank. The installation of the stand 15 in the denitrification tank is optional. By further fastening the stand 15 to the fiber molded body 10, the fiber molded body 10 can be stably positioned in the denitrification tank so that it is always approximately perpendicular to the direction of the wastewater flow. There is no limit to the number of fiber molded bodies 10 that can be fixed to the stand 15. For example, as shown in FIG. 3(b), multiple fiber molded bodies 10 can be fixed to the stand 15 at regular intervals. To increase the efficiency of contact with the air current supplied from the bottom of the denitrification tank, multiple fiber molded bodies may be arranged with a slight offset in the water depth direction.

[0050] The amount of the denitrification agent 100 packed in the denitrification tank can be 5% by volume or more and less than 40% by volume per effective water volume of the denitrification tank. If the packing rate is less than 5% by volume, the contact efficiency between the denitrification agent 100 and the nitrogen-containing wastewater is low, and sufficient denitrification performance may not be achieved. If the packing rate exceeds 40% by volume, the installation of the denitrification agent 100 may cause uneven flow of the nitrogen-containing wastewater or increase the possibility of clogging of the denitrification agent 100. The packing rate of the denitrification agent 100 is preferably 7 to 35% by volume, and more preferably 10 to 30% by volume. The packing rate of the denitrification agent 100 refers to the volume of the fibrous molded body 10 (rayon fibers 11a, 11b, 11c, 11d) constituting the denitrification agent 100 relative to the effective volume of the denitrification tank. That is, it can be expressed as [filling rate of denitrification agent 100]=[volume of fibrous molded body 10 including fiber spaces]÷[effective volume of denitrification tank (amount of water held in denitrification tank)]×100.

[0051] On the other hand, when rayon fibers 11a, 11b, 11c, and 11d constitute a part of the fibrous molding 10, if the filling volume of the rayon fibers 11a, 11b, 11c, and 11d constituting the fibrous molding 10 in the denitrification tank is too small, the denitrification performance may not be significantly improved. On the other hand, if the filling volume is too large, clogging may occur depending on the fiber length of the rayon fibers 11a, 11b, 11c, and 11d. The rayon fibers 11a, 11b, 11c, and 11d may account for, for example, 30 to 100% by volume, more preferably 50 to 95% by volume, of the capacity of the denitrification tank.

[0052] In addition to having denitrification properties, the fibrous molded article 10 can also be used as a microbial carrier. That is, the fibrous molded article 10 according to the embodiment of the present invention can be used not only as a hydrogen donor for denitrification but also as a microbial carrier for biological treatment.

[0053] As described above, the denitrification treatment agent 100 according to the embodiment of the present invention includes the fibrous molded body 10 containing rayon fibers 11a, 11b, 11c, and 11d. As a result, the denitrification treatment agent 100 according to the embodiment of the present invention can suppress the outflow of the fibrous molded body 10 out of the denitrification treatment tank and increase contact with the nitrogen-containing wastewater, while eliminating the need for controlling the injection of the hydrogen donor, and enabling efficient denitrification of nitrogen-containing wastewater with a simple configuration.

[0054] (Method for denitrification of nitrogen-containing wastewater) An example of a treatment flow for nitrogen-containing wastewater that can use the denitrification agent according to an embodiment of the present invention is shown in Figure 4. The method for treating nitrogen-containing wastewater according to the embodiment of the present invention includes a denitrification step in which nitrogen-containing wastewater is introduced into denitrification tank 1, which contains denitrification agent 100 composed of fibrous molded body 10 containing rayon fibers 11a, 11b, 11c, and 11d formed into a specific shape and having a fiber diameter of 100 μm or less, and the nitrogen-containing wastewater is denitrified while being agitated in denitrification tank 1 to bring the nitrogen-containing wastewater into contact with the denitrification agent; and a solid-liquid separation step in which the denitrification liquid obtained in the denitrification step is separated into solid and liquid. A portion of the separated sludge obtained by solid-liquid separation is returned to denitrification tank 1 via returned sludge transfer means 3 as returned sludge, and the remaining separated sludge is discharged to the outside as excess sludge.

[0055] As nitrogen-containing wastewater suitable for the denitrification treatment shown in Figure 4, wastewater containing nitrate nitrogen and nitrite nitrogen but not ammonia nitrogen or organic nitrogen can be used. The nitrogen concentration of nitrogen-containing wastewater is typically 10 to 50 mg / L, and more typically 10 to 30 mg / L. The nitrogen concentration of nitrogen-containing wastewater refers to the total concentration of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen.

[0056] 4, it is preferable that the nitrogen concentration of the nitrogen-containing wastewater is 50 mg / L or less, more preferably 30 mg / L or less, and even more preferably 20 mg / L or less. According to the method for treating nitrogen-containing wastewater of the embodiment of the present invention, in a nitrogen-containing wastewater treatment apparatus equipped with a denitrification treatment tank 1 and a solid-liquid separation tank 2 (solid-liquid separation means), nitrogen-containing wastewater with a nitrogen concentration of 50 mg / L or less is introduced into the denitrification treatment tank 1, and a fibrous molded body 10 is placed therein for biological treatment, thereby enabling more efficient denitrification treatment in the solid-liquid separation tank 2 for a long period of time without the need to inject a hydrogen donor such as methanol.

[0057] The denitrification tank 1 receives nitrogen-containing wastewater and return sludge separated from the solid-liquid separation tank 2 and biologically treats them under aerobic conditions in the presence of denitrifying bacteria. A denitrification agent 100, consisting of a fibrous molded body 10 containing rayon fibers 11a, 11b, 11c, and 11d, is placed in a predetermined position within the denitrification tank 1. This denitrification agent 100 acts as a hydrogen donor, converting nitrate ions in the nitrogen-containing wastewater into nitrogen gas, thereby removing nitrogen from the wastewater. The configuration shown in Figure 4 eliminates the problem of methanol-induced BOD leaching from the denitrification solution, as compared with systems using methanol as a hydrogen donor. Therefore, the aeration tank 1300 shown in Figure 10 can be omitted. Furthermore, the fibrous molded body 10 can be used as a microbial carrier in addition to its denitrification properties. While return sludge is generally required to be supplied to the denitrification tank 1 during initial startup, the supply of return sludge to the denitrification tank 1 can be omitted once denitrification is stabilized and steady-state operation is achieved. Furthermore, even if the return sludge flow rate is reduced compared to conventional methods, stable treatment can be achieved for a long period of time while keeping the MLSS concentration in the denitrification treatment tank 1 low (for example, an MLSS concentration of about 100 to 2000 mg / L).

[0058] As shown in Fig. 5, agitation means 20 is connected to the denitrification tank 1 for agitating the nitrogen-containing wastewater in the denitrification tank 1. The agitation means 20 is provided for the purposes of agitating the contents of the denitrification tank 1 and improving contact between the nitrogen-containing wastewater and the denitrification agent 100. A mechanical agitator such as an agitator blade or a pump agitator is used as the agitation means 20, but from the perspective of simplifying the equipment, it is preferable to use an agitation device equipped with an aeration pipe and a blower that sends air to the aeration pipe, which is capable of simultaneously agitating the contents of the denitrification tank 1 and supplying air to the denitrification tank 1.

[0059] A DO meter 30 is disposed in the denitrification tank 1 to measure the DO of the nitrogen-containing wastewater in the denitrification tank 1. The DO meter 30 may be a commercially available diaphragm type or a fluorescent type. Multiple DO meters 30 may be installed horizontally or in the depth direction of the denitrification tank 1. The DO in the denitrification tank 1 may be measured sequentially by removing the nitrogen-containing wastewater from the denitrification tank 1 using a pump or the like. In the case of an agitation means 20 that supplies air, it is preferable to control the amount of air supplied based on the measurement results of the DO meter 30 so that the denitrification tank 1 has a predetermined BOD sludge load.

[0060] Although not limited to the following, it is preferable to adjust the amount of air introduced into the denitrification treatment tank 1 so that the DO concentration in the denitrification treatment tank 1 is, for example, 0.1 to less than 2.0 mg / L, further 0.2 to less than 1.5 mg / L, and even further 0.2 to less than 1.1 mg / L. If the DO concentration is less than 0.1 mg / L, the contact efficiency between the denitrification treatment agent 100 and the nitrogen-containing wastewater may be insufficient, and ammoniacal nitrogen in the nitrogen-containing wastewater may not be efficiently removed. If the DO concentration exceeds 2.0 mg / L, the denitrification treatment may be insufficient, and nitrate nitrogen in the nitrogen-containing wastewater may not be sufficiently removed.

[0061] A denitrification treatment agent 100 including a fibrous molded body 10 is disposed above the agitation means 20. By disposing the denitrification treatment agent 100 directly above the agitation means 20 and supplying air from the agitation means 20, contact between the denitrification treatment agent 100 and nitrogen-containing wastewater can be improved, further improving denitrification performance. In addition, by introducing air from the bottom of the denitrification treatment agent 100 to generate an upward airflow toward the denitrification treatment agent 100 and causing contact, clogging of the sludge in the fibrous molded body 10 constituting the denitrification treatment agent 100 can be suppressed. As a result, stable denitrification performance can be achieved over a long period of time.

[0062] There are no particular limitations on the number or location of the fiber moldings 10. For example, by arranging the fiber moldings 10 at intervals (shortest distance) of about 20 to 200 mm, more preferably about 30 to 100 mm, between each other, it is possible to increase the contact between each fiber molding 10 and the activated sludge mixed liquid while maintaining a predetermined denitrification performance and improving the effect of preventing the sludge from floating up.

[0063] As shown in FIG. 4 , a solid-liquid separation tank 2, such as a settling tank, is connected downstream of the denitrification tank 1. The biologically treated water in the denitrification tank 1 is separated into solids and liquids by gravitational settling or the like in the solid-liquid separation tank 2, yielding separated sludge and treated water. According to this embodiment, by using the denitrification agent 100 according to this embodiment in the denitrification tank 1, denitrification can be carried out more easily and efficiently than when methanol or the like is injected as a hydrogen donor into the denitrification tank 1. Furthermore, because the nitrite nitrogen and nitrate nitrogen contained in the denitrification liquid obtained in the denitrification tank 1 are removed in advance in the denitrification tank 1, nitrogen gas is less likely to be generated when the denitrification liquid is supplied to the solid-liquid separation tank 2 for solid-liquid separation. Therefore, sludge adhering to the generated nitrogen gas is less likely to float.

[0064] (Nitrogen-containing wastewater treatment device) As shown in Fig. 4, a nitrogen-containing wastewater treatment apparatus according to an embodiment of the present invention includes a denitrification treatment agent 100 composed of a fibrous molded body containing rayon fibers having a fiber diameter of 100 µm or less, a denitrification treatment means (denitrification treatment tank 1) for denitrifying nitrogen-containing wastewater in the presence of denitrifying bacteria, an agitation means 20 (not shown) for agitating the nitrogen-containing wastewater supplied to denitrification treatment tank 1 and bringing the nitrogen-containing wastewater into contact with the denitrification treatment agent 100, and a solid-liquid separation tank means (solid-liquid separation tank 2) for performing solid-liquid separation of the denitrification treatment liquid obtained in denitrification treatment tank 1. A returned sludge transfer means 3 is connected between solid-liquid separation tank 2 and denitrification treatment tank 1. A portion of the separated sludge obtained in solid-liquid separation tank 2 is returned to denitrification treatment tank 1 via the returned sludge transfer means 3, and the remaining separated sludge is discharged outside the treatment system for sludge treatment.

[0065] The denitrification agent 100 can be formed of a fiber molding 10 as shown in FIGS. 1(a) to 1(d). Furthermore, by providing the denitrification agent 100 with a stand 15 as shown in FIGS. 3(a) and 3(b), it can be stably held in a predetermined position in the denitrification tank 1. Furthermore, as shown in FIG. 5, by disposing an agitation means 20 capable of supplying air to the denitrification agent 100 below the denitrification agent 100, clogging of the denitrification agent 100 can be suppressed while agitating the contents in the denitrification tank 1. In FIG. 4, the denitrification tank 1 may be composed of multiple tanks or may be composed of a denitrification tank 1 partitioned into multiple regions. When the denitrification tank 1 is composed of multiple tanks, the denitrification agent 100 is disposed in the latter half of the denitrification tank 1. When the denitrification tank 1 is partitioned into multiple regions, the denitrification agent 100 is preferably disposed at least at an arbitrary location in the latter half of the partitioned region. In this embodiment, the first half and second half refer to the retention time of the nitrogen-containing wastewater, which is calculated by dividing the effective volume of the denitrification treatment tank 1 by the flow rate of the nitrogen-containing wastewater, and the first half of the retention time is the first half, and the remaining half is the second half.

[0066] (First Modification) FIG. 6 shows an example of a method and apparatus for treating nitrogen-containing wastewater according to a first modified embodiment of the present invention. FIG. 6 illustrates an example in which a nitrification step is further performed prior to denitrification treatment using a denitrification agent 100, in which the nitrogen-containing wastewater is nitrified in the presence of nitrifying bacteria. The denitrification treatment apparatus shown in FIG. 6 includes a denitrification tank 1 containing the denitrification agent 100, which is composed of a fibrous molded body 10 formed into a specific shape and containing rayon fibers with a fiber diameter of 100 μm or less; a solid-liquid separation tank 2 for performing solid-liquid separation of the denitrification solution obtained in the denitrification tank 1; and a nitrification tank 5 (nitrification treatment means) provided prior to the denitrification tank 1, which nitrifies the nitrogen-containing wastewater in the presence of nitrifying bacteria. The separated sludge separated in the solid-liquid separation tank 2 is returned to the nitrification tank 5 as returned sludge. The remaining separated sludge is discharged to the outside as excess sludge.

[0067] Nitrogen-containing wastewater suitable for the denitrification treatment shown in Figure 6 includes wastewater containing ammoniacal nitrogen, nitrate nitrogen, nitrite nitrogen, and organic nitrogen. While not limited to the above, the nitrogen-containing wastewater is preferably organic wastewater containing ammoniacal nitrogen, nitrate nitrogen, nitrite nitrogen, and organic nitrogen, typically having a nitrogen concentration of 10 to 50 mg / L, more typically 10 to 30 mg / L. Ammoniacal nitrogen or organic nitrogen is typically contained in an amount of 10 to 50 mg / L, more typically 10 to 30 mg / L. Nitrite nitrogen is typically contained in an amount of 0 to 40 mg / L, more typically 0 to 20 mg / L. Nitrate nitrogen is typically contained in an amount of 0 to 40 mg / L, more typically 0 to 20 mg / L.

[0068] In the nitrification tank 5, ammoniacal nitrogen and organic nitrogen from the nitrogen-containing wastewater are oxidized to nitrate nitrogen and nitrite nitrogen by nitrifying bacteria in the activated sludge in the presence of dissolved oxygen. As nitrification progresses, the pH decreases, which in turn reduces the activity of nitrifying bacteria. Therefore, it is preferable to supply an alkaline agent such as caustic soda to the nitrification tank 5 to adjust the pH in the nitrification tank 5 to 6 to 7.5. Air is supplied to the nitrification tank 5. The amount of air supplied is controlled by monitoring the DO concentration and ammoniacal nitrogen concentration of the nitrified liquor in the nitrification tank 5. The nitrified liquor obtained in the nitrification tank 5 is supplied to the denitrification tank 1, where denitrification is carried out using a denitrification agent 100 contained in the denitrification tank 1. The fibrous molded body 10 constituting the denitrification agent 100 not only has denitrification properties but can also be used as a microbial carrier. As a result, during initial start-up, it is necessary in principle to supply returned sludge to the nitrification treatment tank 5, but during steady-state operation when nitrification and denitrification treatment are stable, stable treatment can be carried out over a long period of time while keeping the MLSS concentration in the nitrification treatment tank 5 and denitrification treatment tank 1 low (for example, MLSS concentration of about 100 to 2000 mg / L) even if the flow rate of returned sludge to the nitrification treatment tank 5 is reduced compared to conventional methods. In addition, keeping the MLSS concentration in the nitrification treatment tank 5 low also has the effect of suppressing nitrification in the nitrification treatment tank 5.

[0069] (Second Modification) Fig. 7 shows an example of a method and apparatus for treating nitrogen-containing wastewater according to a second modified embodiment of the present invention. The denitrification treatment apparatus shown in Fig. 7 is a treatment flow for removing nitrogen from nitrogen-containing wastewater containing organic nitrogen such as BOD, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen, and includes a pre-denitrification treatment step (pre-denitrification treatment tank (first denitrification treatment tank 1a in Fig. 7)) located upstream of the nitrification treatment tank 5, in which the nitrogen-containing wastewater is brought into contact with a denitrification treatment agent 100 made of fibrous molded bodies 10 formed into a specific shape and containing rayon fibers with a fiber diameter of 100 µm or less, and subjected to pre-denitrification treatment in the presence of denitrifying bacteria.

[0070] The first denitrification tank 1a (first denitrification means) receives nitrogen-containing wastewater, returned sludge from the solid-liquid separation tank 2 via the returned sludge transfer means 3, and the activated sludge mixed liquor (hereinafter, "nitrified liquor") returned from the nitrification tank 5. The nitrate and nitrite nitrogen in the nitrified liquor are removed as nitrogen gas by the action of denitrifying bacteria and the BOD of the nitrogen-containing wastewater, resulting in denitrification. The BOD is also removed simultaneously during denitrification. In the first denitrification tank 1a, which contains a denitrification agent 100 using a fibrous molded body 10 as a fixed bed, if the BOD of the nitrogen-containing wastewater is insufficient compared to the nitrate and nitrite nitrogen in the nitrified liquor, the denitrification agent 100 is used as a hydrogen donor after the BOD of the nitrogen-containing wastewater is consumed. In the first denitrification treatment tank 1a, if the BOD of the nitrogen-containing wastewater or the rayon fiber moldings are not sufficient to denitrify the wastewater, a conventional hydrogen donor such as methanol can be added via the hydrogen donor adding means 4.

[0071] In the nitrification treatment tank 5, in the presence of dissolved oxygen, ammoniacal nitrogen and organic nitrogen derived from nitrogen-containing wastewater in the effluent (first denitrification treatment liquid) discharged from the first denitrification treatment tank 1a are oxidized to nitrate nitrogen and nitrite nitrogen by nitrifying bacteria in the activated sludge, and the BOD remaining in the effluent is treated. Air is sent to an aeration device (not shown) at the bottom of the nitrification treatment tank 5. The amount of air supplied is controlled by monitoring the DO concentration and ammoniacal nitrogen concentration of the nitrification liquid in the nitrification treatment tank 5.

[0072] The second denitrification tank 1b (second denitrification means) removes nitrate nitrogen and nitrite nitrogen contained in the nitrified liquor from the nitrification tank 5 as nitrogen gas using denitrifying bacteria and a denitrification agent 100 as a hydrogen donor. Because the nitrate and nitrite nitrogen loads contained in the nitrified liquor are only about 1 / 10 to 1 / 100 of the nitrate and nitrite nitrogen loads of the nitrified liquor flowing into the second denitrification tank 1b, denitrification can be achieved using only the denitrification agent 100 disposed in the second denitrification tank 1b. Furthermore, because the second denitrification tank 1b does not generally produce a denitrified liquor containing residual methanol, an aeration tank for removing residual methanol is generally not required.

[0073] In the solid-liquid separation tank 2, the denitrification treatment liquid (second denitrification treatment liquid) obtained in the second denitrification treatment tank 1b is subjected to solid-liquid separation. The denitrification treatment liquid is separated into separated sludge and treated water, and a portion of the separated sludge, including activated sludge, is returned to the first denitrification treatment tank 1a as returned sludge, while the remaining separated sludge, or excess sludge, is discharged outside the system and undergoes sludge treatment such as dehydration.

[0074] 7 may each be composed of multiple tanks, or may each be composed of denitrification tanks 1a, 1b partitioned into multiple regions. In this case, if denitrification tanks 1a, 1b are composed of multiple tanks, denitrification agent 100 is disposed in the latter half of denitrification tanks 1a, 1b, and if denitrification tanks 1a, 1b are partitioned into multiple regions, it is preferable that denitrification agent 100 is disposed at least at any location in the latter half of the former and latter half of the latter half when the regions are divided into the former and latter half.

[0075] (Third Modification) FIG. 8 shows an example of a method and apparatus for treating nitrogen-containing wastewater according to a third modified embodiment of the present invention. The denitrification treatment apparatus shown in FIG. 8 shows a treatment flow for treating nitrogen-containing sludge containing a high concentration of suspended solids (SS) as nitrogen-containing wastewater. Nitrogen-containing sludge containing a high concentration of SS (suspended solids) of 500 to 30,000 mg / L, such as sewage or septic tank sludge, is coagulated in coagulation tank 6 by adding polymer and inorganic coagulants. The nitrogen-containing sludge coagulates flowing out of coagulation tank 6 and is separated into a dehydrated cake and a separated liquid using a thickener, a dehydrator, or the like in concentration / dehydration treatment means 7 (first solid-liquid separation means). The treatment flow for the separated liquid is the same as that of the denitrification treatment shown in FIG. 7. The excess sludge separated in solid-liquid separation tank 2 (second solid-liquid separation means) is returned to coagulation tank 6 or concentration / dehydration treatment means 7, which are located upstream of concentration / dehydration treatment means 7, via excess sludge return means 8. A portion of the nitrified liquid obtained in the nitrification treatment tank 5 is returned to the first denitrification treatment tank 1 a via nitrified liquid returning means 9 .

[0076] The main components of nitrogen-containing sludge in Figure 8 are nitrogen, SS, and BOD, and because nitrogen-containing sludge is anaerobic, it does not contain nitrate nitrogen or nitrite nitrogen. The nitrogen in nitrogen-containing sludge is ammonia nitrogen, which is involved in nitrification, and organic nitrogen. Nitrogen-containing sludge with a combined ammonia nitrogen and organic nitrogen concentration of over 50 mg / L can be used.

[0077] Typically, the SS of the nitrogen-containing sludge is 500 to 30,000 mg / L, more typically 3,000 to 10,000 mg / L, and even more typically 3,000 to 6,000 mg / L. The BOD of the nitrogen-containing sludge is 100 to 10,000 mg / L, more typically 150 to 5,000 mg / L, and even more typically 200 to 3,000 mg / L.

[0078] In the thickening and dehydration treatment means 7, which is the first solid-liquid separation step, the SS of the nitrogen-containing sludge and the organic matter and nitrogen components contained in the SS of the nitrogen-containing sludge are removed. At the same time, the excess sludge generated in the biological treatment is subjected to solid-liquid separation together with nitrogen-containing sludge such as human waste in the thickening and dehydration treatment means 7, and the SS of the excess sludge and the organic matter and nitrogen components contained in the SS of the excess sludge are removed. Meanwhile, because the thickening and dehydration treatment means 7 has a higher organic matter removal rate than the nitrogen components, the ratio of BOD to total nitrogen in the separated liquid (BOD / TN) is typically less than 3, more typically less than 2.5. Because these BOD and TN values vary significantly depending on the properties of the nitrogen-containing sludge and the operating conditions of the thickening and dehydration treatment means 7, conventional methods have involved adding an excess amount of a hydrogen donor such as methanol and decomposing the remaining methanol in an aeration tank.

[0079] 8, a denitrification agent 100 made of a fibrous molding 10 that functions as a hydrogen donor is placed in the first denitrification tank 1a that receives the separated liquid from the concentration / dehydration means 7, so that denitrification can be performed in the first denitrification tank 1a without injecting methanol as a hydrogen donor. This eliminates the need to adjust the amount of methanol added, simplifies operation management, and also eliminates the need for an aeration tank.

[0080] The denitrification treatment apparatus according to the third modification of the present invention can perform denitrification treatment with a simple configuration, even on nitrogen-containing sludge with a relatively high nitrogen concentration and a high SS concentration, such as sewage or septic tank sludge, without using a hydrogen donor such as methanol or controlling its injection. Furthermore, by returning the separated sludge from the second solid-liquid separation process in the second solid-liquid separation tank 2 to the first denitrification tank 1a, which performs the first denitrification process, and the concentration / dehydration means 7, which performs the first solid-liquid separation process, via the coagulation tank 6, the separated sludge from the second solid-liquid separation process can be effectively utilized to stabilize the biological treatment while reducing the amount of separated sludge discharged and treated outside the system. The return treatment from the solid-liquid separation tank 2 may involve simply supplying the returned sludge to the first denitrification tank 1a, or simply supplying excess sludge to the coagulation tank 6, or both.

[0081] (Fourth Modification) Fig. 9 shows an example of a method and apparatus for treating nitrogen-containing wastewater according to a fourth modified embodiment of the present invention. The denitrification treatment apparatus shown in Fig. 9 is a treatment flow diagram for denitrifying nitrate nitrogen and nitrite nitrogen produced by nitrification of ammoniacal nitrogen and organic nitrogen in nitrogen-containing wastewater in an aerobic denitrification tank 1c using a fibrous molded body containing rayon fiber as a hydrogen donor. That is, in the denitrification treatment apparatus shown in Fig. 9, nitrification and denitrification occur simultaneously under aerobic conditions in the aerobic denitrification step in the aerobic denitrification tank 1c.

[0082] Nitrogen-containing wastewater may contain nitrogen in the form of ammoniacal nitrogen, organic nitrogen, or both, or may contain nitrogen in the form of ammoniacal nitrogen, organic nitrogen, and nitrate nitrogen, or nitrite nitrogen, or nitrate nitrogen and nitrite nitrogen. It may or may not contain BOD.

[0083] In the example shown in Figure 9, nitrogen-containing wastewater is introduced into the aerobic denitrification treatment, and the denitrification treatment agent 100 described above, for example, as shown in Figures 1 and 3, is introduced into the aerobic denitrification treatment. Air is supplied to bring the nitrogen-containing wastewater into contact with the denitrification treatment agent in the aerobic denitrification treatment, and the aerobic denitrification treatment liquid is subjected to solid-liquid separation.

[0084] Nitrogen-containing wastewater and returned sludge from solid-liquid separation tank 2 are introduced into aerobic denitrification tank 1c via returned sludge transfer means 3. Air is then introduced into the bottom of aerobic denitrification tank 1c, in which fiber moldings containing rayon fibers are placed. By this, ammoniacal nitrogen and organic nitrogen in the nitrogen-containing wastewater are oxidized to nitrate nitrogen and nitrite nitrogen by nitrifying bacteria and the like via the rayon fiber moldings. At the same time, the nitrate nitrogen and nitrite nitrogen are converted into nitrogen gas by the action of the hydrogen donor in the rayon fiber moldings and the denitrifying bacteria, thereby removing nitrogen.

[0085] The modified example shown in FIG. 9 can also be used as a finishing nitrogen treatment for nitrogen-containing wastewater treatment, which removes residual ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen from biologically treated organic wastewater. Furthermore, since an aerobic denitrification tank 1c is provided instead of a denitrification treatment device having a nitrification tank, a subsequent denitrification tank, and a reaeration tank, as in typical wastewater treatment systems, the equipment can be simplified. Multiple aerobic denitrification tanks 1c may be arranged in series, or the interior of the aerobic denitrification tank 1c may be partitioned into multiple sections. Furthermore, a denitrification treatment agent made of a fibrous molded article containing rayon fibers may be placed in at least one of the multiple aerobic denitrification tanks 1c. Furthermore, the denitrification treatment agent may be placed in any of the multiple sections partitioned into the interior of the aerobic denitrification tank 1c.

[0086] Air is introduced from below the denitrification treatment agent containing the fibrous molded body placed in the aerobic denitrification tank 1c to agitate the mixed solution in the aerobic denitrification tank 1c and supply DO. The air flow rate is controlled by the DO of the mixed solution in the aerobic denitrification tank 1c. The amount of air introduced into the aerobic denitrification tank 1c is adjusted so that the average DO concentration of the mixed solution in the aerobic denitrification tank 1c is 0.2 to 1.0 mg / L.

[0087] The purpose of the air is to agitate the aerobic denitrification tank 1c, improve contact between the denitrification agent and the 100 mixed solution, and prevent clogging and drift of the rayon fibers due to sludge accumulation on or inside the fibrous molded body that constitutes the denitrification agent 100. The agitating air can be from below the fibrous molded body of the denitrification agent 100, from the bottom of the tank where the denitrification agent 100 is not located, or both. A DO concentration of the mixed solution in the aerobic denitrification tank 1c of 0.2 or higher ensures sufficient agitation within the tank, maintaining nitrification and denitrification performance. A DO concentration of the mixed solution in the aerobic denitrification tank 1c of 1.0 mg / L or less prevents clogging of the rayon fiber molded body, maintaining nitrification and denitrification performance. Furthermore, the fibrous molded body 10 can be used as a microbial carrier in addition to its denitrification performance. Therefore, during initial startup, it is generally necessary to supply return sludge to the aerobic denitrification tank. Furthermore, by using the fiber molding 10, during steady-state operation when the aerobic denitrification treatment is stable, stable aerobic denitrification treatment can be performed for a long period of time while keeping the MLSS concentration in the aerobic denitrification treatment tank low, even if the return sludge to the aerobic denitrification treatment tank is omitted or the return sludge flow rate is reduced compared to conventional methods.

[0088] Although the present invention has been described with reference to the above-described embodiments, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. The present disclosure is not limited to the above-described embodiments, and components can be combined and modified to be embodied within the scope of the gist of the present disclosure. [Example]

[0089] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0090] Example 1 Nitrified sludge collected from the nitrification tank of the sludge reclamation center's nitrification and denitrification treatment facility was sieved with a 2-mm mesh sieve to remove impurities and used as seed sludge (SS 8,000 mg / L). This seed sludge was introduced into the denitrification treatment tank 1 of a simulation test device corresponding to the nitrogen-containing wastewater treatment device shown in Figure 4, and a biological treatment test was conducted using nitrogen-containing wastewater produced at a beverage manufacturing plant as the simulated test wastewater. Table 1 shows the specifications and treatment conditions of the test device. Note that the hydrogen donor loading rate in Table 1 refers to the loading rate of the denitrification treatment agent according to the embodiment of the present invention, specifically, the ratio of the total volume of the entire fiber molded body made of rayon fiber to the effective capacity of the denitrification treatment tank 1. As shown in Table 1, the hydrogen donor loading rate ranges from 0 to 60 L. When the hydrogen donor is loaded into the denitrification treatment tank, the volumetric loading of nitrate and nitrite nitrogen (NOx-N volumetric loading) is 0.3 to 2.7 kg / m. 3 Treatment was carried out so that the hydrogen donor was 1000 times the amount of HCl.

[0091] [Table 1]

[0092] A treatment tank with a width of 0.5 m, length of 0.5 m, and effective depth of 0.6 m was used for denitrification treatment tank 1. The simulated test wastewater was prepared by adding sodium nitrate reagent to nitrification / denitrification treatment liquid (pH 7.2, SS 2.3 mg / L, ammonia nitrogen concentration 0.5 mg / L, nitrate nitrogen concentration 0.1 mg / L, nitrite nitrogen concentration 0.1 mg / L) collected from the settling tank of the nitrification / denitrification treatment facility at the sludge reclamation center, to bring the nitrate nitrogen concentration to 20 mg / L, and further adding phosphoric acid reagent as a nutrient to bring the phosphorus concentration to 2.0 mg / L.

[0093] Treated water volume: 0.15m 3 / day, and the nitrified sludge from which impurities have been removed is used as seed sludge. The MLSS in the denitrification tank is adjusted to 4000 mg / L, the liquid temperature is 20-25°C, and the pH of the denitrification tank mixed liquid is adjusted to 6.5-7.0 with a 5 wt% aqueous sulfuric acid solution and a 5 wt% aqueous sodium hydroxide solution. The nitrate nitrogen volume load is 0.3-2.7 kg-N / m 3 A continuous denitrification experiment was carried out using three types of fibrous pellets as hydrogen donors.

[0094] Air was supplied from the bottom of the fiber molding to the mixed solution in the denitrification tank so that the DO of the mixed solution was 0.2 mg / L, and the mixed solution was brought into contact with a hydrogen donor as a denitrification treatment agent according to this embodiment to perform denitrification. The hydrogen donors used in the test were as follows:

[0095] Hydrogen donor (1): A fiber molded product (10 mm thick, 500 mm long, 400 mm wide, manufactured by Daiwabo Rayon Co., Ltd.) made by processing rayon fibers with a fiber diameter of 40 μm into a felt-like shape was fixed on a stainless steel wire mesh with a mesh opening of 3 mm (volume excluding the wire mesh: 2.0 L, weight: 0.4 kg), and 4 to 60 pieces of this were fixed in the center of the denitrification treatment tank. Hydrogen donor (2): Short rayon fibers (Evagrose (registered trademark) U-710, manufactured by Suing Co., Ltd.) with a fiber diameter of 40 μm and a fiber length of 10 mm were fixed to a stainless steel wire mesh with a mesh opening of 3 mm (volume excluding the wire mesh: 2.0 L, weight: 1.0 kg) and fixed to the center of the denitrification treatment tank. Hydrogen donor (3): Lauric acid (Lunac L-98, Kao Chemicals) was formed into tablets (volume 0.000098 L, weight 0.000083 kg) with a diameter of 5 mm and a height of 5 mm using a tablet press. The lauric acid tablets were filled into a cylindrical stainless steel wire mesh (thickness 100 mm, length 500 mm, width 400 mm) with a mesh opening of 3 mm (volume excluding the wire mesh: 20 L, weight 1.6 kg) and fixed in the center of a denitrification tank. The denitrification test results are shown in Table 2.

[0096] [Table 2]

[0097] The nitrate nitrogen content of treated water with hydrogen donor (1) at a loading rate of 5% by volume and 40% by volume was 0.3 mg / L, and at a loading rate of 13 to 30% by volume it was 0.1 mg / L. The nitrate nitrogen content of treated water with hydrogen donor (2) at a loading rate of 5% by volume and 40% by volume was 0.5 mg / L, and at a loading rate of 13 to 30% by volume it was 0.1 mg / L. The nitrate nitrogen content of treated water with hydrogen donor (3) at a loading rate of 13 to 30% by volume was 2.9 mg / L or more. The hydrogen donors (1) and (2) according to this example were able to suppress ammonia nitrogen in the treated water to 0.1 to 0.2 mg / L and nitrate nitrogen to 0.1 mg / L or less.

[0098] Example 2 The simulated test wastewater was prepared by adding sodium nitrate reagent to the same nitrification / denitrification treatment solution as in Example 1 (pH 7.2, SS 2.3 mg / L, ammonia nitrogen concentration 0.5 mg / L, nitrate nitrogen concentration 0.1 mg / L, nitrite nitrogen concentration 0.1 mg / L) to adjust the nitrate nitrogen concentration to 20 mg / L, and further adding phosphoric acid reagent as a nutrient to adjust the phosphorus concentration to 2.0 mg / L.

[0099] Using the same test equipment as in Example 1, nitrification and denitrification were carried out simultaneously in a single biological treatment process. An aerobic denitrification process simultaneously treated ammoniacal nitrogen, nitrate nitrogen, etc., and an ammoniacal nitrogen sludge load of 0.03 kg-N / kg-day and a DO concentration of 1.0 mg / L was carried out for approximately two weeks. After this, the treated water had ammoniacal nitrogen of 0.1 mg / L, nitrate nitrogen of 15 mg / L, and a nitrite nitrogen concentration of 0.1 mg / L, indicating that most of the ammoniacal nitrogen had been nitrified.

[0100] After the seed sludge was acclimatized in the denitrification tank of Example 1, the hydrogen donor (2) was filled at 20% by volume, and the ammoniacal nitrogen load was 0.7 kg-N / m 3Denitrification tests were conducted using a hydrogen donor and DO concentrations of 0.1 to 2.0 mg / L. Two weeks after the start of the test, when denitrification had stabilized, the DO concentration of the mixed solution in the denitrification tank was varied and the ammonia nitrogen and nitrate nitrogen in the treated water were measured. Note that, since the inside of the test equipment in Example 1 was completely mixed with air, the DO of the mixed solution in the denitrification tank was measured near the center of the water depth on the side of the fiber extrusion, where it was not directly exposed to air bubbles. Table 3 shows the results of the aerobic denitrification test.

[0101] [Table 3]

[0102] A hydrogen donor (2) consisting of a fibrous molded body containing rayon fibers filled at a 20% volume ratio was placed inside the test apparatus of Example 1. The fibrous molded body was used as both a hydrogen donor and a biological carrier, successfully denitrifying simulated test wastewater with an ammonia nitrogen concentration of 20 mg / L. When the average DO concentration of the mixed liquor in the denitrification tank was 0.1 mg / L, the treated water had ammonia nitrogen of 1.2 mg / L and nitrate nitrogen of less than 0.1 mg / L, indicating somewhat insufficient nitrification and a relatively large amount of ammonia nitrogen remaining. When the average DO concentration of the mixed liquor in the denitrification tank was 0.3 to 1.0 mg / L, the treated water had ammonia nitrogen of less than 0.1 mg / L to 0.2 mg / L and nitrate nitrogen of less than 0.1 mg / L to 0.8 mg / L, indicating good nitrification and denitrification. When the average DO concentration of the mixed liquor in the denitrification tank was 1.4 mg / L, the ammonia nitrogen in the treated water was 0.1 mg / L, which was good for nitrification, but the nitrate nitrogen was high at 5.0 mg / L, which resulted in slightly poor denitrification.When the average DO concentration of the mixed liquor in the denitrification tank was 1.8 mg / L, the nitrate nitrogen concentration was high at 18 mg / L, which resulted in even poorer denitrification. [Explanation of symbols]

[0103] 1. Denitrification tank 1a First denitrification tank 1b Second denitrification tank 1c Aerobic denitrification tank 2 Solid-liquid separation tank 3 Return sludge transport means 4. Hydrogen donor addition means 5. Nitrification tank 6 Coagulation tank 7 Concentration and dehydration treatment methods 8. Excess sludge return means 9 Nitrification liquid return means 10 Fiber molding 11, 11a, 11b, 11c, 11d Rayon fiber 12a, 12b, 12c, 12d, 13a, 13d Support 15 Mounting stand 20 Stirring means 30 DO meter 100 Denitrification Treatment Agent 500 Nitrification treatment tank 1100 Denitrification tank 1300 Aeration tank 2000 Solid-liquid separation tank

Claims

1. A denitrification treatment agent used for denitrification treatment of nitrogen-containing wastewater, characterized in that it is composed of a fibrous molded body molded into a specific shape and containing rayon fibers with a fiber diameter of 100 μm or less.

2. 2. The denitrification treatment agent according to claim 1, wherein the fiber molding comprises a support for supporting the rayon fibers, and the fiber molding has any one of the following shapes: rectangular parallelepiped, cubic, cylindrical, columnar, block, plate, membrane, lattice, or string-like shape formed by bundling both ends of the rayon fibers.

3. Nitrogen-containing wastewater is introduced into a denitrification treatment tank containing a denitrification treatment agent composed of a fibrous molded body molded into a specific shape containing rayon fibers with a fiber diameter of 100 μm or less, The nitrogen-containing wastewater is denitrified while being brought into contact with the denitrification agent by stirring the contents in the denitrification treatment tank; The denitrification treatment liquid obtained by the denitrification treatment is subjected to solid-liquid separation. A denitrification treatment method characterized by the above.

4. Nitrogen-containing wastewater is nitrified in the presence of nitrifying bacteria, The nitrified liquid obtained by the nitrification treatment is poured into a denitrification treatment tank containing a denitrification treatment agent composed of a fibrous molded body molded into a specific shape containing rayon fibers with a fiber diameter of 100 μm or less, agitating the denitrification treatment tank to bring the nitrification liquid into contact with the denitrification treatment agent, and denitrifying the nitrification liquid in the presence of denitrifying bacteria; The denitrification treatment liquid obtained by the denitrification treatment is subjected to solid-liquid separation. A denitrification treatment method characterized by the above.

5. 5. The denitrification method according to claim 4, wherein the nitrogen-containing wastewater is subjected to a denitrification treatment before the nitrification treatment.

6. a first solid-liquid separation treatment for separating nitrogen-containing sludge into solid and liquid; a first denitrification treatment in which the separated liquid obtained in the first solid-liquid separation treatment is poured into a first denitrification treatment tank containing a denitrification treatment agent composed of a fiber molding formed into a specific shape containing rayon fibers having a fiber diameter of 100 μm or less, and the first denitrification treatment tank is stirred to denitrify the separated liquid while bringing the separated liquid into contact with the denitrification treatment agent; a nitrification treatment in which the first denitrification treatment liquid obtained by the first denitrification treatment is nitrified in the presence of nitrifying bacteria; a second denitrification treatment in which the nitrified liquid obtained by the nitrification treatment is introduced into a second denitrification treatment tank, and the nitrified liquid is denitrified in the second denitrification treatment tank in the presence of denitrifying bacteria; a second solid-liquid separation treatment for performing solid-liquid separation on the second denitrification treatment liquid obtained by the second denitrification treatment; a return process in which the separated sludge separated in the second solid-liquid separation process is returned to at least one of the first denitrification process and the first solid-liquid separation process; A denitrification treatment method comprising:

7. Nitrogen-containing wastewater is introduced into the aerobic denitrification treatment system. A denitrification treatment agent comprising a fibrous molded body formed into a predetermined shape containing rayon fibers with a fiber diameter of 100 μm or less is introduced into the aerobic denitrification treatment, In the aerobic denitrification treatment, air is supplied to bring the nitrogen-containing wastewater into contact with the denitrification treatment agent; The aerobic denitrification treatment liquid is subjected to solid-liquid separation. A denitrification treatment method characterized by the above.

8. a denitrification treatment means for denitrifying nitrogen-containing wastewater in the presence of denitrifying bacteria, the denitrification treatment means comprising a denitrification treatment agent made of a fibrous molded body formed into a specific shape and containing rayon fibers with a fiber diameter of 100 μm or less; a stirring means for stirring the nitrogen-containing wastewater supplied to the denitrification treatment means and bringing the nitrogen-containing wastewater into contact with the denitrification treatment agent; a solid-liquid separation means for separating the denitrification treatment liquid treated by the denitrification treatment means into solid and liquid; A denitrification treatment device comprising:

9. nitrification treatment means for introducing nitrogen-containing wastewater and nitrifying it; a denitrification treatment means for denitrifying the nitrified liquid obtained by the nitrification treatment means in the presence of denitrifying bacteria, the denitrification treatment agent being a denitrification treatment agent made of a fibrous molded body formed into a specific shape and containing rayon fibers with a fiber diameter of 100 μm or less; a stirring means for stirring the nitrified liquid and bringing the nitrified liquid into contact with the denitrification treatment agent to obtain a denitrification treatment liquid; a solid-liquid separation means for separating the denitrification treatment liquid into solid and liquid; A denitrification treatment device comprising:

10. a first denitrification treatment means comprising a denitrification treatment agent made of a fibrous molded body formed into a specific shape and containing rayon fibers having a fiber diameter of 100 μm or less, and which denitrifies nitrogen-containing wastewater or nitrogen-containing sludge in the presence of denitrifying bacteria to obtain a first denitrification treatment liquid; nitrification treatment means for nitrifying the first denitrification treatment liquid; a nitrification solution return means for returning the nitrification solution obtained by the first denitrification treatment means; a second denitrification treatment means for contacting the nitrification solution obtained by the nitrification treatment means with a denitrification treatment agent composed of a fibrous molded body formed into a specific shape and containing rayon fibers having a fiber diameter of 100 μm or less, to obtain a second denitrification treatment solution; a solid-liquid separation means for performing solid-liquid separation on the second denitrification treatment liquid to obtain return sludge to be returned to the first denitrification treatment means; A denitrification treatment device comprising:

11. a concentration / dehydration treatment means for dehydrating and concentrating the nitrogen-containing wastewater or the nitrogen-containing sludge, which is provided in a stage preceding the first denitrification treatment means; an excess sludge returning means for returning the excess sludge obtained by the solid-liquid separation means to a coagulation tank provided in a stage preceding the concentration and dehydration treatment means or to the concentration and dehydration treatment means; The denitrification treatment apparatus according to claim 10, further comprising:

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